1. Field of the Invention:
This invention relates to improvements to tools for tightening or non-destructive removal of threaded fasteners from objects, and particularly for removing studs protruding from objects sufficiently to grasp the studs about their circumference and to apply torquing force to rotate them. Still more particularly, this invention relates to sockets designed to axially surround the stud with gripping jaws which automatically contact the stud simultaneously in multiple locations about its circumference to apply thereto angular torque generated by a driver such as an impact wrench.
2. Description of Related Art:
Studs are lengths of rod threaded on one or both ends which serve as fasteners between objects in similar fashion to bolts. Unlike bolts, however, studs usually have no hexagonal head or other fixture adapted to cooperate with conventional wrenches for applying torque to the fixture to turn the bolt. Screwing or unscrewing threaded studs into or out of objects typically requires a tool adapted to apply angular torque to the axial perimeter of the stud at a point between the object and the end of the stud. Common hand tools adapted for the purpose include pipe wrenches which employ opposing toothed jaws to bite into the stud when angularly displacing an elongated, radially extending handle to apply angular force to the stud. Other hand tools, chucks or grapples employ different numbers of such jaws, three being the most common, radially forced against the stud using cams, as illustrated by U.S. Pat. No. 3,371,562.
Impact wrenches employing pneumatic pressure produce impulsed angular force to overcome frictional resistance to rotation of the stud. Sockets for use with impact wrenches commonly rely upon differential rotation between the socket and a vehicle bearing gripping jaws and carried within an axially aligned cavity in the socket. Cams on the cavity walls mate with outer curved surfaces of the jaws as the socket rotates to bias the jaws radially inward and into frictional contact with the outer perimeter of the stud. Teeth borne on the inner surface of the jaws bite into the stud to enhance the gripping effect of the frictional contact.
For various reasons, available sockets provide less than satisfactory performance of this function. For example, Merrick, U.S. Pat. Nos. 4,932,292 (Merrick I), and 5,152,195 (Merrick II), provide a plurality of jaws held within an open ended socket and biased outward against the cams by springs. Merrick I provides a positioning ring at one end of a trio of jaws, each of which has a lug protruding longitudinally into a radial slot within the ring. The positioning ring shifts with the jaws within the cavity to permit the radial slots to define and maintain balanced angular positioning of the jaws. Springs within the slots bear radially outward against the lugs to force open the jaws and to permit insertion of a stud into the cavity between the gripping surfaces of the jaws. Because of inevitable unbalanced tortional forces between each of the jaws, however, the lugs tend to shear off during rotational operation. This largely renders the tool inoperable because the jaws collapse inward and prevent insertion of a stud or fall out of place altogether.
Merrick II ostensibly offers an improvement by substituting for the positioning ring a hollow, cylindrical cage adapted to rotate with the jaws within the socket cavity. The cage carries one jaw within each of two opposing windows communicating through the cage walls. A resilient, circular wire forming a split-ring spring biases the jaws outward, the wire being carried in an annular groove longitudinally bifurcating the gripping surface of the jaws and the inner surface of the cage. If excess force is applied, however, such as where a stud is particularly hard to break out, the cage tends to continue its angular shift relative to the socket even after the jaws have gripped the stud and ceased shifting. This condition causes the jaws to slip out of the windows, further causing the cage to slip beneath one edge of the gripping surface of the jaws. This in turn applies radial force against the jaw, breaking either the jaw, the cage or both. A need therefore exists for a jaw configuration which will not break under adverse operating conditions and which has a reliable means to bias the jaws radially outward against the cams when not in use.
An additional problem of "bolt lock" arises with Merrick II and with any other such device employing one or more pairs of directly opposing jaws, especially where only two are present. The preferred method of loosening the jaws for removal of the socket from the stud is by simply reversing the torque applied by the driver. The cams thereby should reverse their angular shift relative to the jaws, increasing the radius of the socket walls at their contact with the jaws and decreasing the pressure applied until the gripping surface can slip on the stud. The biasing spring then fully retracts the jaws. When two opposing jaws lock into a grip on the stud, however, the radial forces applied by the cams directly oppose each other. This locks the cams to their bearing surface on the jaws, thereby locking the jaws to the stud and preventing loosening the jaws by reversing the torque. As reversing torque is applied, the tangential force in the socket walls at the cam contact point with the jaw is likely to cause the jaws to try to travel with the socket walls instead of causing the socket to turn relative to the jaws to relieve the pressure. If the jaws have shifted past this frictional "point of no return", reversing the torque only further forces the cam against the jaws, increasing the radial force against the jaws and the stud rather than decreasing it to permit the gripping surfaces to slip and unlock the grip. Giving the jaws a graduated thickness from one sidewall to the other helps deter bolt lock but does not prevent it, because sufficient thickness gradient to do so would create significant resultant tangential components to the biasing force of the cams, increasing shear forces applied to the stud and encouraging undesirable slippage of the teeth against the stud during operation. A large thickness gradient also requires unacceptably greater radial socket size to stud diameter. A need exists for a jaw configuration that functions effectively within a rotating socket without causing bolt lock.
Extraction of very large, heavy studs, such as those in the housing of turbine generators, often requires assistance of a crane to lift the studs using a sling or other device provided for the purpose. Likewise, the extraction tool for the job is heavy and, together with the driver, usually must be lifted into place using a crane. Field personnel have a tendency to use the extraction tool to lift the stud, however, without attaching the safety lifting sling. This creates a hazard that the jaws will spontaneously loosen and drop the stud, causing injury or damage. Such lifting is possible because radial forces tend to create significant friction between the cams and the jaws, even if the condition of bolt lock has not occurred. Nothing in the design of known socket jaw configurations prevents jostling from overcoming this friction and permitting the jaws to slip. A need therefore exists for a means of preventing reliance on the gripping surface to lift the stud.